1. Field of the Invention
This invention relates to a method of and a system for producing NC machining data for machining a product by a numerically controlled machine tool on the basis of, for instance, a three-dimensional shape model produced by a CAD (computer aided design).
2. Description of the Prior Art
Recently there has come into wide use an automatic programming system for controlling a numerically controlled machine tool by the use of a computer.
As such an automatic programming system, there have been known an APT, EXAPT, AUTOSPOT, FAFT and the like. The APT calculates geometric tool paths and can calculates the tool paths of a simultaneous multiple spindle control machine tool. The EXAPT can calculate the working condition of a drilling machine, a lathe or the like in addition to the tool path thereof. When controlling the numerically controlled machine tool by the automatic programming system, a numerical control tape must be produced, and in order to produce the numerical control tape, a part program must first be prepared. The part program is a program in which how the tool is moved is written in the language of the system. The prepared part program is input into a main processor and is used in a geometric operation, whereby CL (Cutter Location) data, in which the tool paths are expressed using a generalized coordinate system, are obtained. Thereafter, the CL data are input into a postprocessor and are converted into a machine coordinate system, thereby corrected to values which conform to the tape format of the numerically controlled machine tool. Then predetermined NC (numerical control) codes such as G, F, T, M and the like are inserted.
However the part program cannot be directly obtained from a three-dimensional design data of a product shape model produced by a CAD. This is because though such a three-dimensional design data includes therein data on the position of each machined portion and, for example, when the machined portion is a hole, the position of the center of the hole can be read from the three-dimensional design data, the three-dimensional design data includes no data on the attribute of the machining to be carried out, such as those from which whether the hole is a reamed hole, or a threaded hole can be known. Accordingly, the operator must determine the attribute of the machining to be carried out for each portion and the part program is prepared by combining the attribute of the machining determined by the operator with the data on the position of each machined portion. Therefore, in the conventional system, it takes a very long time to prepare the part program, and further the part program must be converted into CL data and the CL data further must be converted into NC codes.
Further since the part program includes the data on the position of each machined portion, the part program must be prepared for each kind of product.